Serial communication networks provide many advantages over other well-known networks such as multipoint, star or mesh networks, the most valuable being a fair distributed polling function which readily supports peer-to-peer communications amongst a large number of stations with a high utilization of the network capacity.
One major drawback of the serial network is its propensity to catastrophic failure when any component of the network fails.
Over the years many techniques have been developed to detect and/or isolate faults in serial communication networks. One of the more useful techniques, which is in use today in the IEEE 802.5 Token Ring, is disclosed in U.S. Pat. No. 3,564,145. This technique known as beaconing identifies a station, by its address, immediately down stream of a failed network component or station. In a static network (e.g. one in which the network topology is fixed or known) corrective action can be taken to bypass or fix the failed network component.
Another technique (Dual Ring Reconfiguration) has proven very useful in the isolation of faults in a serial network, thereby providing complete or partial network operation following the failure of a network component. This technique employs dual serial rings which may be converted to single ring via switching means to thereby bypass a failed network component. The patents listed below disclose a variety of Dual Ring Reconfiguration implementations:
______________________________________ U.S. Pat. No. 3,519,750 U.S. Pat. No. 4,527,270 U.S. Pat. No. 3,876,983 U.S. Pat. No. 4,538,264 U.S. Pat. No. 4,009,469 U.S. Pat. No. 4,594,790 U.S. Pat. No. 4,354,267 U.S. Pat. No. 4,709,365 U.S. Pat. No. 4,390,984 ______________________________________
The patents listed below disclose a variety of manual and automatic techniques for bypassing a failed network component in a single ring serial network:
U.S. Pat. No. 3,458,661 PA1 U.S. Pat. No. 4,035,770 PA1 U.S. Pat. No. 4,048,446 PA1 U.S. Pat. No. 4,245,343 PA1 U.S. Pat. No. 4,763,329
While all of the techniques described above are useful either by themselves or in combination, they are unable to provide fast, efficient or complete restoration of communications in a serial ring network following failures of all kinds.
Modern serial networks such as the IEEE 802.5 Token Ring Network generally employ many (up to several hundred or more) ports located throughout an establishment. Many of these ports are not utilized or are connected to inactive stations. In addition, stations (each of which includes a unique identity or address) are frequently moved from one port to another for the convenience of the operator.
In view of the mobility of the stations and the large number of ports which have no or inactive stations connected, the station identity or address accompanying a beacon message provides little information to locate the geographic position of the failed network component.
The technique (Next Active Upstream Neighbor) disclosed in U.S. Pat. No. 4,507,777 is very useful in managing fault recovery in serial networks; however, the sequential station identities or addresses derived from this technique do not provide sufficient network topology information to accurately pinpoint the physical location of the failed component. For example, two adjacent active stations may be separated on the physical network by a number of non-connected or inactive ports. Thus, knowing that station X detected a failure and that station C preceded X does not physically locate a particular faulty component.
Current serial ring communication networks have no automated provision for developing an accurate network topology which accurately associates each physical port with the identity or address of an active station connected thereto. Two solutions, neither of which is practical, have been considered. Each station upon activation could input its identity or address along with a network defined location to a database or manager. This task could be accomplished manually by an operator. This is a burdensome task and would require cooperative human operators at every station. On the other hand, sufficient intelligence could be provided at each port to automatically provide the location information either to the station for automatic transmittal to a database or network manager or directly when a station connected thereto becomes active. Such a solution is impractical from a cost standpoint alone.